Gap coupled symmetric split ring resonator based near zero index ENG metamaterial for gain improvement of monopole antenna

In this article, a symmetric split ring resonator (SRR) based metamaterial (MTM) is presented that exhibits three resonances of transmission coefficient (S21) covering S, C, and X-bands with epsilon negative (ENG) and near zero index properties. The proposed MTM is designed on an FR4 substrate with the copper resonator at one side formed with two square rings and one circular split ring. The two square rings are coupled together around the split gap of the outer ring, whereas two split semicircles are also coupled together near the split gaps. Thus, gap coupled symmetric SRR is formed, which helps to obtain resonances at 2.78 GHz, 7.7 GHz and 10.16 GHz with desired properties of the MTM unit cell. The MTM unit cell's symmetric nature helps reduce the mutual coupling effect among the array elements. Thus, different array of unit cells provides a similar response to the unit cell compared with numerical simulation performed in CST microwave studio and validated by measurement. The equivalent circuit is modelled for the proposed MTM unit cell in Advanced Design System (ADS) software, and circuit validation is accomplished by comparing S21 obtained in ADS with the same of CST. The effective medium ratio (EMR) of 10.7 indicates the compactness of the proposed MTM. A test antenna is designed to observe the effect of the MTM over it. Numerical analysis shows that the proposed MTM have an impact on the antenna when it is used as the superstrate and helps to increase the gain of the antenna by 95% with increased directivity. Thus, compact size, high EMR, negative permittivity, near zero permeability and refractive index makes this MTM suitable for S, C and X band applications, especially for antenna gain with directivity enhancement.

www.nature.com/scientificreports/ side help to modify the resonance frequency, and bandwidth as its length significantly affects both. The proposed antenna shows a wide bandwidth with marginal gain. But, when the proposed metamaterial is used with the antenna, significant gain enhancement is achieved within a broad bandwidth, verified through the experiments.

Design of metamaterial and equivalent circuit modeling
This section includes a discussion on the proposed MTM that consists of the substrate material properties, resonating patch structure, simulation set up, step by step design process of MTM with the change of transmission and reflection coefficient. Furthermore, since the MTM unit cell exhibits multiband resonances indicating that the unit cell acts as LC resonance circuit, the equivalent circuit is also modeled and designed with validation using ADS in this section.
Design and simulation of the proposed MTM. The proposed metamaterial(MTM) unit cell is designed on FR-4 substrate of 1.6 mm thick having a dielectric constant value of 4.3 with a loss tangent value of 0.025. The resonating patch is constructed at one side of the substrate using a copper metal having 0.035 mm thick. The MTM is originated on the substrate having a dimension of 10 × 10.5 mm 2 . As shown in Fig. 1a, the resonating patch is constructed with three split rings, the outer two are square-shaped, and the innermost one is circular. Two outer rectangular SRRs are coupled together by using metal strips at both ends of the split gaps of the outermost ring, as shown in Fig. 1a. Moreover, parallel inductive paths are created by coupling two ends of split gaps of the innermost circular ring. All these couplings contribute significantly to the resonances when electromagnetic waves are imposed on the MTM. Each SRR ring's dimension is selected, and the slip gaps and coupling metal strips are so positioned that the whole structure becomes axis-symmetric. The symmetric nature of the MTM helps to eliminate the harmonics and mutual coupling effect between the array elements when an array of the unit cells are employed for different uses. Table 1 presents the parameter values of different segments of the proposed MTM of Fig. 1a. The parameter values shown in Table 1 are finalized with numerous numerical simulations performed for the frequency ranges 2-12 GHz in CST microwave studio suite-2019 to obtained triple-band resonances of transmission coefficient (S 21 ). The simulation arrangement in CST is presented in Fig. 1b, where two waveguide ports are used in Z-axis. In this arrangement, transverse electromagnetic (TEM) signal transmitted from one waveguide port incidents perpendicularly on the resonating patch. After transmitting through the MTM, the transmitted signal is received by another port. The electrical boundary is employed in X-axis in the simulation arrangement, on the other hand, the magnetic boundary is used in the Y-axis. The TEM waves represent a particular class of guided waves with neither E field component nor H filed component in the direction of propagation, meaning that E z = H z = 0 along the Z-axis. When this wave is incident upon the metamaterial, the response of the material depends on its properties such as permittivity, permeability. The time varying electric and magnetic flux densities in the material can be interrelated with the time varying electric and magnetic field using the mathmetical relations presented in Ref. 37 which helps to understand the impact of the medium on some important parameters such as refractive index, wavenumber, and wave  www.nature.com/scientificreports/ impedance. Electromagnetic field coupling occurs in a medium as time-varying electric charges are the sources of the magnetic fields, generating electric fields varied with time. These relations can be expressed through Maxwell's equations presented in the differential form in Ref. 37 . The Maxwell's equations indicate the coexistance of oscillating electric and magnetic fields, which initiates electromagnetic waves that travel through the medium. Now, when the incident wave is imposed upon the MTM, electromagnetic induction occurs and resonating phenomena is experienced as the split rings of it acts as resonantor. Thus the split ring resonator (SRR) can be demonstrated by an equivalent resonant circuit containg inductance, L and capacitance, C that offers resonances at some frequencies of SRR. The proposed MTM is designed through numerous numerical simulations with the modification of the length and width of different rings, and split gap distances since these parameters have an dominating impact on the resonance phenomena of the MTM. Moreover, inter ring distances and their interconnections are modified through trial and error basis to obtain the expected outcomes. Thus, the design finalization of the proposed MTM unit cell undergoes several design steps started with a square copper ring having two split gaps at vertical arms as displayed in design 1 of Fig. 2. This single ring causes a resonance of transmission coefficient (S 21 ) taking place at 4.02 GHz, as shown in Fig. 3a. In design two, another square split ring is added that holds two splits at horizontal arms and square blocks at each corner, as illustrated in design 2 of Fig. 2. This insertion causes another addition resonance of S 21 holding at 13.3 GHz. Moreover, owing to the mutual coupling between these two rings, primary resonance shifts slightly to 4.1 GHz. In the next step, one additional circular-shaped split ring is introduced (presented in design 3 of Fig. 2) that includes other resonances along with frequency shifts of the previous two resonances as consisted at 4.02 GHz, 11.43 GHz, and 14.5 GHz, as shown in Fig. 3a. In the succeeding step, two half circles of the innermost rings are coupled near the split gaps by using shunt copper strips as shown in design 4 of Fig. 2 with an effect of shifting of mid and high-frequency resonances at 10.02 GHz and 13.2 GHz as depicted in Fig. 3a. In the final step, two outermost rings are coupled adjoining the outmost ring's gaps as illustrated in the proposed MTM of Fig. 2 with a formation of gap coupled symmetric split ring resonator MTM. This gap coupling causes shifting in the resonances at 2.78 GHz, 7.7 GHz and 10.16 GHz with an increasing effective medium ratio. Thus, the proposed MTM provides triple-band resonances within C, S, X-bands. The S 21 response of the MTM for all design phases are also mentioned in Table 2, whereas reflection coefficients (S 11 ) plots are presented in Fig. 3b for various design steps.
The effect of different design steps is further analyzed through field analysis (magnetic and electric) and study of current at MTM at a particular frequency of 4.02 GHz, where resonance for design 1 occurs. As expressed in Fig. 3c shown in design 1, the horizontal sides of the outermost ring is susceptible to the magnetic field, and magnetic dipoles are created when electromagnetic waves are incident on the SRR, which in turn creates the current dipole with current flowing clockwise and anticlockwise through this two edges of outer ring. Electric field spreading is oriented in the vertical sides and forms an electric dipole. Therefore, magnetic and electric dipoles are linked to each other, and electromagnetic resonances of S 21 occur at 4.02 GHz. In design 2, as extra ring is inserted inside earlier ring, this not only causes an additional resonance at 13.3 GHz but also modifies earlier resonance at 4.1 GHz. This is because of the mutual inductance and co-planar capacitance presented in Eqs. (7) and (8), respectively. This effect is evident from Fig. 3c, as it is noticed the opposite flowing currents through the inner ring compared to the outer ring. This opposition effect is dominant at four corners. Thus, this current causes a mutual inductance to the outer ring causing the modification of the total inductance and resonance frequency to 4.2 GHz. The electric field and magnetic field distribution for design 2 in Fig. 3c also exhibits the change compared to the same distribution of design 1. In design 3, an additional inner ring causes to reduce the mutual coupling effect on the outer ring; thus first resonance is restored at 4.02 GHz, whereas it has an impact on the second ring as shown electric and magnetic field distribution in design 3 of Fig. 3c. Design 4 has less impact on the field distribution at 4.02 GHz whereas, gap coupling in the proposed design modifies the current, www.nature.com/scientificreports/ CST. This is due to the fact that in the proposed MTM the inductance and capacitance are distributed all over the design domain. In contrast, in the equivalent circuit model, the components are considered lumped. Moreover, the resistive effects of the copper strips and inter-ring capacitances are ignored, which is distributive in nature.

Result analysis of the proposed MTM
This section comprises various property analyses of the proposed MTM along with electromagnetic field and current distribution studies. Moreover, array performance is also studied as cluster of MTM cells arranged in a regualar pattern is utilized in many applications. Furthermore, the obtained result in measurement is also conferred, and an analysis is made on the presented MTM in comparison with other recent works on the MTM.
Effective parameter analysis. The MTM property has been extracted by using CST post processing template that uses transmission (S 21 ) and reflection coefficient (S 11 ) coefficients to calculate permittivity, permeability and refractive index with the help of robust method where scattering parameters are concerned with by 40 : www.nature.com/scientificreports/ where (.)′ is real part, (.)″ is the imaginary part, m is an integer associated to real part of refractive index. Two other effective parameter permeability and permittivity can be calculated by using the equations: By using Eqs. (7)-(9) the effective parameters are determined using post processing module in CST. The result obtained from the CST related to scattering parameters, permeability, permittivity and refractive index are depicted in Fig. 6a (1) Permittivity, ε = n/z. www.nature.com/scientificreports/ Surface current, electric field and magnetic field analysis. The interaction of the electromagnetic wave with the metamaterial and its effects on resonances can be realized by analyzing various fields (electromagnetic) and current. Figure 7 shows the surface current spreading at 2.78 GHz and 10.16 GHz. In contrast, magnetic field and electric field distribution at these frequencies are presented in Figs. 8 and 9, respectively. The interrelation between various fields and currents can be explained with the help of Maxwell's equations 37 . As shown in Fig. 7a, a strong surface current flows through the outermost ring at 2.78 GHz. The lower and upper halves of these ring currents form a circular current with the second ring though the current density in the   www.nature.com/scientificreports/ second ring is low. The upper current loop forms circulating current in the anticlockwise direction, whereas the lower loop bears current in clockwise current. These currents induce a strong magnetic field surrounding the outer ring, as displayed in Fig. 8a. Likely, Fig. 9a shows the corresponding electric field distribution, indicating that a strong electric field exists at two vertical arms forming the electric dipoles triggering the resonance at 2.78 GHz. At this frequency, a strong magnetic field also exists at different portions of the middle ring and nearest portions of the middle and inner rings. At 10.16 GHz, the surface current is strong at the boundaries of the innermost ring, and lower and upper half current flows in the opposite directions, as shown in Fig. 7b. This surface current induces magnetic fields at the periphery of the innermost ring, as depicted in Fig. 8b. A strong electric field exists adjacent to the horizontal sides and gap coupling stips of the innermost ring (shown in Fig. 9b), indicating the contribution of the innermost ring for the resonance at 10.16 GHz.
Array analysis and measurement. As in many pragmatic cases, the array of the unit cells works together for particular applications rather than solitary unit cell and so, outcomes of array is analyzed using 2 × 2 and 4 × 4 arrays of MTM cells. The S 21 and S 11 obtained from this study are depicted in Fig. 10a,b, respectively. Comparing the array performances with the unit cell indicates that array results are well matched with the unit cell. The substantial similarity is owing to the fact that the MTM cell is symmetric in the structure; thus, when several cells are organized in a regular pattern in an array, the electromagnetic field near the adjacent side does not affect much. Therefore, it avoids harmonics and resonance frequency shifts. Since unit cell response and array response of the metamaterial are similar, so measurement result is taken by fabricating a 2 × 2 array. The fabricated prototype is shown in Fig. 11a, whereas measurement arrangement is presented in Fig. 11b. In the measurement setup in Fig. 11b, two waveguide ports are employed as a transmitter and receiver of the electromagnetic waves that are    It is also observed from this figure that some amount of noise and harmonics exist at the low and mid-frequency in the measured S 21 . Moreover, measured S 21 deviates from simulation one in terms of resonance frequencies and magnitude at resonance, but this mismatching is not significant. Fabrication tolerances, coupling effect in the waveguide ports and calibration errors in VNA are the reasons for this mismatching. Despite minor mismatch and harmonics, the measured result is well agreed with the simulation results covering the S, C and X-bands.

Comparative analysis.
A comparison is made of the proposed MTM unit cell with some recent works where MTMs are designed to target various applications, summarized in Table 3. In this comparison, physical and electrical dimensions of the applied MTM, Transmission coefficient resonance frequencies, effective medium ratio (EMR), covering bands are considered major parameters. Moreover, special features along with the applications are also discussed in this comparison. EMR is calculated at the lowest resonance frequency of S 21 using the relation, EMR = /L , where is the wavelength at the lowest resonance frequency of S 21 and L is the highest dimension of the MTM unit cell. From  www.nature.com/scientificreports/ specific range of frequencies. Although MTM in Ref. 28 covers X, C and Ku bands, no particular application is presented. All the other MTMs presented in Refs. [44][45][46][47] in Table 3 lag behind physical size, EMR values, and the number of covering bands. Thus, the proposed MTM covers multiples bands with high EMR values within its moderate dimension that provides the flexibility of application in small dimension devices in wireless communication with a diversity of operating in the wider frequency range. Moreover, its negative permittivity property with near zero refractive index and permeability makes it suitable for gain enhancement verified with numerical analysis in the next section.

Design and simulation of the test antenna
A monopole antenna is designed consisting of a slotted patch with partial ground and parasitic elements in the backside, as shown in Fig. 13. The designed antenna is initiated on an FR4-substrate with 1.6 mm thickness and 4.3 dielectric constant. The overall dimension of the antenna is 40 × 41 mm 2 and has a patch of 22 × 26 mm 2 . At the same time, a feedline of width 2.96 mm is used to match the impedance to 50 Ω. Various slots in the patch are used to control the current flowing through the patch to obtain the wideband response with sufficient gain and efficiency of the antenna 48 . Figure 13a shows the geometry of the patch of the antenna, whereas Fig. 13b shows the structural geometry of the ground plane. The different parameter values of the various slots and segments in patch and grounds are listed in Table 4. The partial ground structure helps to obtain an omnidirectional radiation pattern, whereas slots in the ground plane along with the inverted L shaped parasitic elements help to improve the bandwidth. Figure 14a shows the reflection coefficient of the antenna that expresses the bandwidth extended from 2.5 to 4.24 GHz, with two resonances occurring at 2.6 GHz and 3.77 GHz. Moreover, the efficiency and gain presented in Fig. 14b indicates that the average efficiency is more than 80% within this band, and the antenna's average gain is 2 dBi with maximum efficiency of 88% and a maximum gain of 2.95 dBi. The slots inside the patch modify the direction of the current flow and lessen the patch's dimension 49 or help to improve the impedance bandwidth 50 . The effects of various slots on resonance phenomena surface current analysis can be done for two different frequencies of resonances at 2.6 GHz and 3.77 GHz. Figure 15 shows the current distribution at the patch and ground side of the antenna. As expressed in Fig. 15a, it is noticed that current is more concentrated near the vertical edges of the patch and edges of the inner slots. Larger current path due to inner slot helps to increase the effective inductive reactance. Thus, it causes to obtain the resonance frequency at   Fig. 15a) for this frequency of resonance shows that parasitic elements have a high concentration of currents. In contrast, the ground plane offers a lower dense current. Unlikely, as shown in Fig. 15b, at 3.77 GHz, patch current is mainly concentrated at the vertical edges of the patch, whereas surrounding the inner slot, the current is drastically reduced compared to the current of earlier resonance. Due to the reduced current path, the inductance associated with the patch is lessened, which ultimately affects the resonance at this frequency. A closer look at the ground plane current (in Fig. 15b) shows  www.nature.com/scientificreports/ that current density at both parasitic elements is significantly higher compared with the current through the same elements at 2.6 GHz. A high-intensity current is noticed in the ground plane at the top horizontal edges and through slots in the ground plane. Moreover, all over the ground plane, the current density is high as compared to the current flowing through the ground at 2.6 GHz. Thus, it can be concluded that the current surrounding the inner slot of the patch contributes significantly to the resonance at 2.6 GHz. In contrast, resonance at 3.77 GHz is mainly governed by the current flowing through the backplane slots.

Gain enhancement of antenna using MTM superstrate with antenna
A metamaterial array is introduced, having a 4 × 4 array with the overall dimension of 41 mm × 40 mm to use it as a superstrate. This array element provides the same area of the designed antenna that covers the total surface of the antenna. Thus, it interacts with the most emitted radiation of the antenna, which ultimately helps to improve the gain of the antenna. Figure 16 shows the MTM with the antenna in which MTM array is placed as superstrate at the ground side of the antenna at spacing of 30 mm. The space is selected by parametric study targeting that position of MTM array will not affect the bandwidth of the antenna much rather it will increase the gain. Figure 17 shows the parametric study for various distances between antenna and MTM cover. The S 11 response of the antenna showed in Fig. 17a for different distances between antenna and MTM. As shown in Fig. 17a, the antenna shows dual-band resonances when h = 10 mm for the low distance. As the value of h increases, lower band resonance frequency seems to maintain a constant value with increasing magnitude with distance. But in the case of the upper band, magnitude and resonance frequency shift with increasing the distance. As the distance increases, the upper band resonance frequency decreases gradually with the increasing distance. Eventually, two different bands come closer and combine, and a wideband response is perceived when h = 30 mm or higher. A comparison of antenna gain with MTM for different values of h is made, and the gain plots are depicted in Fig. 17b. As expressed in Fig. 17b, high gain is observed when the distance between the antenna and MTM is low and decreases gradually with the increasing distance. It is because when the distance between the antenna and MTM is low, most of the radiated field impinges on the MTM. Thus more directional radiation is obtained due to the near zero property of the MTM. As the distance increases, more radiated field propagates  www.nature.com/scientificreports/ through the free space and thus, MTM faces less radiation to make its direction, resulting in a decreased gain. Therefore, from this parametric analysis, an optimum distance of 30 mm is considered that provides a considerable bandwidth extended from 2.5 to 3.96 GHz with a moderate amount of enhanced gain. A comparison of S 11 of the antenna with and without MTM is presented in Fig. 18a. It is observed that bandwidth is decreased for the antenna with MTM with a downward shift of upper cutoff frequency. It can be explained by using the impedance matching of the equivalent circuit of the antenna as impedance, Z and frequency, f of resonance can be expressed 51 as, Z = 1 jωC+1/1/jωL and f = 1 2π √ LC respectively, in which L corresponds to total inductance and C is the capacitance. Introducing the MTM with antenna causes a modification of the total capacitance, thus resonance frequency shifts. As the distance between antenna and MTM is low, MTM causes the reduction of the total capacitance of the antenna equivalent circuit, which eventually causes the higher resonance frequency, as shown in Fig. 17a. Contrarily, an increasing distance effects as changing resonances towards lower frequencies.
A comparison of the gain for the antenna with and without MTM superstrate is shown in Fig. 18b that indicates a high gain with MTM superstrate. MTM cover provides a maximum gain of around 4.95 dBi, whereas bared antenna offers a maximum gain of around 2.5 dBi, indicating a gain enhancement by 95%. The gain enhancement can be explained with the help of the electric field (E) distribution in space and on the antenna. This distribution of the E fields at 3.77 GHz is presented in Fig. 19a,b, respectively. Figure 19a shows that electric field strength increases significantly surrounding the antenna when metamaterial is introduced. Moreover, when a radiated field is exposed over MTM, it emits radiation due to its NZI property which is normal to the surface of the MTM. Additionally, EM waves that incidents on the MTM contain a sideward E component that becomes more directional due to the NZI property, which added an extra field in a particular direction. Thus, antenna gain increases significantly. A comparison of the E field distribution over the antenna is shown in Fig. 19b. This figure shows a strong E field induced at the top of the antenna when MTM is used with the antenna. This strong E field is also the contributor to the gain enhancement. Thus, MTM superstrate causes to increase the directionality as well as radiated power that combinedly enhances the overall gain of the antenna. Figure 20a shows the 3D radiation pattern at 3.77 GHz for the antenna without MTM that is omnidirectional in nature. When MTM superstrate is used, the radiation pattern becomes directional as shown in Fig. 20b. The radiation is more concentrated in the Z direction, increasing the antenna's directional gain when MTM superstrate is used.
The result obtained in the simulation is verified by fabricating the antenna and taking the measurement for S 11 and gain. Figure 21a shows the front view of the antenna prototype, whereas Fig. 21b exhibits the back view. Morevoer, antenna with metamaterial superstrate arrangement is presented in Fig. 21c where 4 × 4 array of unit cells of the proposed MTM is seperated from the antenna using a 30 mm thick polystyrene block. The experimental arrangement for S 11 is depicted in Fig. 22a, in which a vector network analyzer (VNA) is used for measuring this parameter. The measured values of the S 11 for antenna with and without metamaterial is depicted in Fig. 23a in comparison with outcomes of simulation. From Fig. 23a, it is noticed that measured results of the antennas with and without metamaterail exhibits close similarity. The measured − 10 dB impedance bandwidth of the test antenna without MTM is exteded from 2.56 to 4.2 GHz with a resonance peak at 3.5 GHz having magnitude of − 17 dB. When MTM is used as the superstrate − 10 dB bandwidth is observed extending from 2.58 to 4.1 GHz with resonance peak of -24 dB at 3.67 GHz. In both cases, the bandwidth is slightly less than the simulation result, but the deviations are less than 5%. This slight variation is associated with fabrication tolerances, calibration errors involved in VNA, and loss incurred in the cable connecting VNA and the antenna prototype. But neglecting these errors fabricated antenna provides good bandwidth when metamaterial superstrate is used. Figure 22b shows the Satimo nearfield measurement setup for the antenna with MTM superstrate to determine the performance parameters, including gain and radiation pattern. Corresponding gain data is plotted in Fig. 23b to compare measured gain with an antenna without MTM and simulation results. This result shows that measured antenna gain with and without metamaterial is slightly varied compared to the simulation result. This mismatching is due to fabrication tolerances of the antenna and calibration errors associated with the Satimo near field measurement system. Measured antenna gain is less compared compared to the simulated      Fig. 24, it can be stated that the radiation pattern shows an omnidirectional type for the antenna with low cross-polarization. On the otherhand, for antenna with metamaterial presented in Fig. 25, the pattren shows slightly directional towards + z directions with low cross polarizations due to gain enhancement by using metamaterial array. The performance of the proposed antenna with MTM superstrate is compared with some other recently published MTM loaded antennas, and the comparison outcomes are presented in Table 5. From Table 5, it is observed that the antenna with MTM superstrate presented in Ref. 52 provides a good maximum gain of 6.56 dBi with an operating resonance frequency at 2.4 GHz. But the overall dimension of the antenna system is large compared to our proposed antenna system. Moreover, the bandwidth of this antenna system is low compared, and metamaterial helps to increase the gain by 22.37%. As is viewed from this Table 5, Ref. 53 shows a comparatively high gain with good percentage enhancement due to the MTM superstrate. But the overall dimension of the MTM array and antenna is high, and this gain is achieved by using four layers of MTM superstrates. Moreover, this antenna operates at a high frequency with a comparatively low bandwidth. In Ref. 54 , the triangular-shaped antenna array is used for two ports MIMO system that exhibits the highest gain of 14.05 dBi. But, this high gain is due to an antenna structure of large size. In this antenna system, a comparatively low gain enhancement is acquired when MTM array is used as a superstrate. Contrary to this, the dimension of the antenna system presented in Ref. 55 exhibits lower dimension, moderate antenna gain, with good gain enhancement due to MTM superstrate. But the high gain within the lower dimension is achieved by using two layers of superstrate. Thus, comparing these

Conclusion
This paper presents a metamaterial consisting of a resonator patch of a symmetric split ring resonator coupling around the split gaps. This proposed MTM provides three resonances at 2.78 GHz, 7.7 GHz, and 10.16 GHz covering S, C, and X-bands. Due to symmetric structure, mutual coupling between the array elements is reduced, and  www.nature.com/scientificreports/ the array shows a similar S 21 response of the unit cell. The simulated result is evaluated with the experiment, and the measured result is well matched with the simulation. The equivalent circuit of the MTM is modeled in ADS and validated by comparing the S 21 response with CST that provides close similarity. The MTM characteristics are also analyzed that show negative permittivity, near zero permeability, and refractive index. The contribution of the different parts of the MTM unit cell in resonance is also studied through the electric field, magnetic field and surface current analysis. The calculated EMR value of 10.7 indicates the compactness of the proposed MTM for application in various small microwave devices. A test antenna having − 10 dB bandwidth of S 11 extending from 2.5 to 3.95 GHz with maximum gain around 2.5 dBi is designed, and MTM influence is observed by using a 4 × 4 array of MTM as superstrate. MTM superstrate over the test antenna provides a maximum gain of 4.95 dBi with an increment by 95% when the distance between antenna and MTM is 30 mm. NZI property of the proposed ENG metamaterial increases the directionality of the radiation in the XZ plane, which is studied through E field and radiation pattern analysis. The antenna gain enhancement is validated by measuring the performance of the antenna with and without metamaterials. Due to its compactness with high EMR, negative permittivity, near zero permeability and refractive index, proposed MTM can be utilized with various wireless devices in microwave applications, especially to enhance gain and directivity of the antenna.